import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		int n = Integer.parseInt(sa[0]);
		int m = Integer.parseInt(sa[1]);
		int p = Integer.parseInt(sa[2]);
		sa = br.readLine().split(" ");
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sa[i]);
		}
		br.close();

		for (int i = 0; i < n; i++) {
			if (a[i] > m) {
				System.out.println(1);
				return;
			}
			while (a[i] % p == 0) {
				a[i] /= p;
			}
		}
		int max = 0;
		for (int i = 0; i < n; i++) {
			max = Math.max(max, a[i]);
		}
		if (max <= 1) {
			System.out.println(-1);
		} else {
			long x = 1;
			int ans = 0;
			while (x <= m) {
				ans++;
				x *= max;
			}
			System.out.println(ans);
		}
	}
}